Elongate tubular members or devices such as needles, stents, catheters, etc., are used extensively in modern medicine for a variety of purposes. For example, such elongate devices are used for medicant delivery, biopsy, mechanical treatment of tissues, removal or relief of occlusions, pressure reduction, and the like. Usually precise positioning of the device is critical to achieve the desired result. However, accurately targeting and intersecting a particular internal location in a three-dimensional body is a challenging endeavor.
Placement of the device is frequently performed manually. The physician relies on external landmarks, knowledge of anatomy, experience, and skill to accurately place the device. More recently, developments in medical imaging technologies, such as computed tomography imaging, magnetic resonance imaging, and ultrasound imaging, have provided some capability for image-guided placement of catheters in particular body locations. In rare instances real-time medical imaging may be available during placement of the catheter. In other instances a previously obtained image may be available as a guide for catheter placement.
Although image-guided catheter placement is efficacious, medical imaging systems are typically not readily available, especially during emergent procedures. Modern medical imaging devices are expensive to purchase and to operate, are time consuming to set up, and usually are fixed or, at best, only semi-portable. These imaging systems typically require considerable training and specialized skills to operate. In particular, these imaging systems are frequently not available in intensive care units, emergency rooms, or pre-hospital settings.
Even if a real-time imaging system is available, however, the imaging system requires the surgeon to orient the stylet while looking at a monitor rather than looking at the stylet itself, further complicating accurate placement of the device. In addition, some such systems require two individuals to perform the combined imaging/catheter-insertion procedure when used simultaneously, simply because two hands are generally required to guide the catheter, and at a minimum one hand is required to run the real-time imaging system.
An example of a medical procedure that would benefit from improvements in the accurate placement of a catheter is ventriculosotomy, or the placement of an external ventricular drain (EVD). In the human brain the ventricular system includes a set of ventricles or interior volumes that produce and contain cerebrospinal fluid (CSF). The ventricles are interconnected with small flow paths (e.g., foramina), and the system is fluidly connected with the central canal of the spinal cord. The CSF flows from the lateral ventricles, through the third and fourth ventricles, and into the central canal of the spinal cord or the subarachnoid space. If the flow paths become blocked, for example, due to infection or the like, pressure within the ventricular system can rise, which can result in injury, for example, hydrocephalus.
An EVD is a catheter used in neurosurgery to relieve elevated intracranial pressure when the normal flow of CSF is obstructed. The EVD catheter is placed over a stiff guide wire or stylet that the surgeon uses to implant the catheter in the patient's brain. A small hole is cut through the skull, and the EVD catheter is inserted through the brain dura mater and into the interior of the brain until it enters the target ventricle.
Freehand placement of the EVD catheter requires the neurosurgeon to estimate the three-dimensional location of the target ventricle, usually based on external anatomical landmarks. The ventricle is typically only about 1 cm across, and may be located at a depth of 5 cm or more. Once the position of the target ventricle is estimated, the EVD catheter is urged through the brain toward the target ventricle. The freehand method does not provide any means to account for potential irregularities in the patient anatomy that are not apparent externally. Factors such as intracranial lesions, genetic variability, and the like, can also affect the location of the target ventricle.
Understandably, freehand placement of EVD catheters has a high failure rate, often requiring the physician to make multiple attempts, resulting in more than one pass through the brain tissue to accomplish the requisite placement of the EVD catheter. In a retrospective study, Toma et al. (2009, Neurosurgery 65:1197) demonstrated that 65% of catheter placements in the setting of inserting ventriculo-peritoneal shunts ended up outside of the target ventricle, with almost half of those requiring revision and reinsertion. Possible complications associated with misplacement of an EVD catheter can include intra-cerebral hemorrhage, stroke, damage to adjacent brain structures, as well as the need for re-operation to replace the malpositioned catheter. Higher infection rates are also reported when multiple EVD placement attempts are required.
Catheterization is a relatively common procedure and has applications in addition to EVD, including ventriculo-peritoneal shunt placement, central venous catheter placement, hemodialysis, epidural anesthesia, lumbar puncture, and the like.
There is a need for low-cost, easy to operate, and portable devices and methods for providing guidance to medical personnel to facilitate inserting elongate tubular members such as needles, stents, catheters, through tissue and into a body.